1. Field of the Invention
The present invention relates to a frequency error measuring method and a frequency error measuring device which are preferably used for measuring a frequency error of a communication waveform in a mobile communication apparatus compatible with a digital communication system.
2. Description of the Related Art
Recently, with the advance of mobile communication techniques, the number of persons carrying a mobile communication apparatus such as a portable telephone is rapidly increasing. In conventional mobile communications, the radio frequency band is defined depending on the kind of the mobile communication system (analog or digital system). The number of channels which can be simultaneously used in communications is set in accordance with the defined radio frequency band.
In recent mobile communication systems, a digital system in which many channels can be efficiently set even in the same radio frequency band is mainly employed. A portable telephone and a portable information communication apparatus having a mobile communication function which are compatible with such a digital mobile communication system, are widely used.
As a digital communication system, for example, employed is the TDMA (Time Division Multiple Access) system, or recently the CDMA (Code Division Multiple Access) system. In a communication device of such a digital system, measurement items include a measurement of a frequency error.
As a conventional method of obtaining a frequency error, known is the phase trajectory method. In the phase trajectory method, a frequency error is obtained from a time-varying deviation between the phase variation of an input signal and that of an ideal phase component.
Conventionally, a phase detector is used as an apparatus for obtaining a frequency error based on the phase trajectory method. Such a phase detector is configured so that the phases of I and Q components of a synchronous-detected input signal are detected, and a result of a frequency error calculation is output by the phase trajectory method in which a frequency error is obtained from differences between the phases and a reference phase difference.
When a frequency error of a xcfx80/4-shift QPSK modulation signal is to be measured in a conventional system, for example, the measurement range of a frequency error is only about {fraction (1/10)} of the transmission rate. When a signal contains a frequency corresponding to {fraction (1/10)} of the transmission rate, therefore, a phase component corresponding to the frequency is added, a symbol point is erroneously detected, and hence a phase difference cannot be correctly obtained, thereby producing a problem in that the measurement accuracy of a frequency error is impaired.
It is an object of the invention to provide a frequency error measuring device in which, even when a frequency error is equal to or greater than {fraction (1/10)} of the transmission rate, the measurement accuracy can be improved.
According to the invention, the object can be attained by employing the following means.
1. A rough frequency of an input modulation signal which is to be measured is obtained by frequency spectrum analyzing means; a predetermined synchronous detection frequency is determined on the basis of the rough frequency; a difference between the synchronous detection frequency and a reference signal is obtained; an I signal and a Q signal are obtained by performing synchronous detection by using the synchronous detection frequency; a frequency error is obtained from the I component and the Q component by a phase trajectory method; and the frequency error is added to the difference, whereby a final frequency error value can be obtained (first aspect of the invention).
2. A rough frequency of an input modulation signal which is to be measured is obtained by frequency spectrum analyzing means; the rough frequency is compared with predetermined upper and lower limit values, and one of plural predetermined synchronous detection frequencies is determined on the basis of a result of the comparison; a difference between the synchronous detection frequency and a reference signal is obtained; an I signal and a Q signal are obtained by performing synchronous detection by using the synchronous detection frequency; a frequency error is obtained from the I component and the Q component by a phase trajectory method; and the frequency error is added to the difference to obtain a final frequency error value (second aspect of the invention).
3. A rough frequency of an input modulation signal which is to be measured is obtained by frequency spectrum analyzing means; the rough frequency is compared with predetermined upper and lower limit values, and one of plural predetermined synchronous detection frequencies is determined on the basis of a result of the comparison; an I signal and a Q signal are obtained by performing synchronous detection by using a sampling data and the synchronous detection frequency, the sampling data being obtained by sampling the modulation signal; a phase data is calculated from the I component and the Q component, and a frequency error is obtained by a phase trajectory method; a difference between the synchronous detection frequency and a reference signal is obtained; and the frequency error is added to the difference; whereby a final frequency error value can be obtained (third aspect of the invention).
4. A rough frequency of an input modulation signal which is to be measured is obtained by frequency spectrum analyzing means; a range in which the rough frequency exists is judged with respect to predetermined upper and lower limit values, a synchronous detection frequency in the case where the frequency is lower than the lower limit value is determined, a synchronous detection frequency in the case where the frequency is higher than the upper limit value is determined, or a synchronous detection frequency in the case where the frequency is between the upper and lower limit values is determined; detection is performed by using a sampling data and the synchronous detection frequency, at a timing of the synchronous detection, thereby obtaining an I signal and a Q signal of the synchronous-detected input signal, the sampling data being obtained by sampling the modulation signal; a phase data is extracted from the I component and the Q component by an atan (arctangent) calculation, and then subjected to a predetermined normalization process, and a frequency error is thereafter obtained by a phase trajectory method from a difference between the phase data and an ideal phase shift point; a difference between the synchronous detection frequency and a reference signal is obtained; and the frequency error is added to the difference; whereby a final frequency error value can be obtained (fourth aspect of the invention).
5. Also in the case where, in the first to fourth aspects of the invention, the frequency spectrum analyzing means is a sweeping spectrum analyzer, a final frequency error value can be obtained (fifth aspect of the invention).
6. Also in the case where, in the first to fourth aspects of the invention, the frequency spectrum analyzing means is an FFT spectrum analyzer, a final frequency error value can be obtained (sixth aspect of the invention).
7. When the means of the first to sixth aspects of the invention is employed, also in the case where the input modulation signal which is to be measured is a xcfx80/4-shift QPSK modulation signal, a final frequency error value can be obtained (seventh aspect of the invention).
8. The device is configured by: a frequency spectrum analyzer which obtains a rough frequency of an input modulation signal which is to be measured; a judging section which determines one of plural predetermined synchronous detection frequencies on the basis of the rough frequency; an adder which obtains a difference between the synchronous detection frequency and a reference signal; a quasi-synchronous detector which performs synchronous detection by using the synchronous detection frequency to output an I signal and a Q signal; a frequency error detector which obtains a frequency error from the I component and the Q component by a phase trajectory method; and an adder which adds the frequency error and the difference (eighth aspect of the invention).
9. The device is configured by: a frequency spectrum analyzer which obtains a rough frequency of an input modulation signal which is to be measured; a judging section which performs judgment on the rough frequency to determine a frequency that is to be subjected to synchronous detection; a sampling data memory which stores the modulation signal to be measured; a quasi-synchronous detector which performs synchronous detection on the modulation signal which is to be measured, by using the frequency which is determined by the judging section; a frequency error detector which calculates phase data from components of the synchronous-detected signal, and which obtains a frequency error from a phase difference between the phase data by a phase trajectory method; and an adder which obtains a difference between the synchronous-detected frequency and a reference frequency, and which adds a measurement result of the frequency error detector to the difference (ninth aspect of the invention).
10. The device is configured by: a frequency spectrum analyzer which obtains a rough frequency of an input modulation signal which is to be measured; a judging section which compares the rough frequency with predetermined upper and lower limit values, and which determines one of plural synchronous detection frequencies on the basis of a result of the comparison; an adder which calculates a difference between the frequency and a reference signal; a quasi-synchronous detector which performs synchronous detection by using the synchronous detection frequency to output an I signal and a Q signal; a frequency error detector which obtains a frequency error from the I component and the Q component by a phase trajectory method; and an adder which adds the frequency error and the difference (tenth aspect of the invention).
11. The device is configured by: a frequency spectrum analyzer which obtains a rough frequency of an input modulation signal which is to be measured; a judging section which compares the rough frequency with predetermined upper and lower limit values, and which determines one of plural synchronous detection frequencies on the basis of a result of the comparison; an adder which calculates a difference between the synchronous detection frequency and a reference signal; a quasi-synchronous detector which performs synchronous detection by using a sampling data and the synchronous detection frequency to output an I signal and a Q signal, the sampling data being obtained by sampling the modulation signal; a frequency error detector which calculates a phase data from the I component and the Q component, and which obtains a frequency error (E) by a phase trajectory method; and an adder which adds the frequency error and the difference (twelfth aspect of the invention).
12. The device is configured by: a frequency spectrum analyzer which obtains a rough frequency of an input modulation signal which is to be measured; a judging section which judges a range in which the rough frequency exists, with respect to predetermined upper and lower limit values, and which determines a synchronous detection frequency in the case where the frequency is lower than the lower limit value, a synchronous detection frequency in the case where the frequency is higher than the upper limit value, or a synchronous detection frequency in the case where the frequency is between the upper and lower limit values; an adder which obtains a difference between the synchronous detection frequency and a reference signal; a quasi-synchronous detector which performs synchronous detection by using a sampling data and the synchronous detection frequency, at a timing of the synchronous detection, and which outputs an I signal and a Q signal of the synchronous-detected signal, the sampling data being obtained by sampling the modulation signal; a frequency error detector which extracts a phase data from the I component and the Q component by an atan (arctangent) calculation, which performs a predetermined normalization process, and obtains a frequency error by a phase trajectory method from a difference between the phase data and an ideal phase shift point; and an adder which adds the frequency error to the difference (fourteenth aspect of the invention).
13. The device is configured by the means of the eighth to twelfth aspects of the invention, and a sampling data memory which stores the modulation signal to be measured (eleventh, thirteenth, and fifteenth aspects of the invention).
14. When the means of the eighth to thirteenth aspects of the invention is employed, also in the case where the input modulation signal which is to be measured is a xcfx80/4-shift QPSK modulation signal, a final frequency error value can be obtained (sixteenth aspect of the invention).
15. In the means of the eighth to twelfth aspects of the invention, the frequency spectrum analyzer is a sweeping spectrum analyzer (seventeenth aspect of the invention).
16. In the means of the eighth to twelfth aspects of the invention, the frequency spectrum analyzer is an FFT spectrum analyzer (eighteenth aspect of the invention).
17. In a frequency error detector of the conventional art and using the phase trajectory method, only a frequency error corresponding to about {fraction (1/10)} of the transmission rate about the local frequency to be subjected to synchronous detection can be obtained at the maximum. By contrast, the frequency error measuring device which performs synchronous detection on signal components contained in an input modulation signal to be measured, calculates a phase data from the synchronous-detected signal components, detects a phase difference between the phase data, and obtains a frequency error by the phase trajectory method is characterized in that the frequency of the input modulation signal is roughly obtained in advance by a frequency spectrum analyzer 2, and the local frequency can be changed to a range where a measurement by the phase trajectory method is enabled.
18. The frequency of an input modulation signal is roughly obtained by a frequency spectrum analyzer 2, and the frequency result is supplied to a judging section 3. The frequency B of synchronous detection is determined by a judging circuit included in a frequency detector. By using the synchronous detection frequency B which is determined by the judging section 3, synchronous detection is performed on a modulation signal A which is to be measured and which is input into a quasi-synchronous detector 5, and I and Q components D are output.
The device is characterized in that, the I and Q components D are input into a frequency error detector 6. In the frequency error detector 6, phase components are extracted, and a frequency error E is obtained by the phase trajectory method. In an adder 8, the obtained frequency error E is added to the difference between the synchronous detection frequency B which is determined by the judging section 3, and a reference frequency, thereby obtaining the correct frequency error of the modulation signal A to be measured.
19. The invention is characterized in that the rough synchronous detection frequency B is rapidly obtained by the frequency spectrum analyzer 2 (first to eighteenth aspect of the invention).